The Patient Core will perform screening diagnosis and laboratory studies on patients in order to identify individuals who will serve as material for the studies in Project 1 (Dr. Terhorst), Project 2 (Dr. Geha) and Project 3 (Dr. Alt). B cell lines, T cell lines and fibroblasts will be prepared from patients suspected of having X-linked lympho proliferation disorders (XLP), patients with T+B- severe combined immunodeficiency (SCID), and of T-B- autosomal recessive SCID. The core will also screen for mutations in the XLP, SLP76- and RAG genes in appropriate patients by protein and sequence analysis. The significance of identified mutations will be studied in functional assays. The FACS section of the core will support the analysis of lymphocytes from knockout and transgenic mice generated in all 3 projects of C. Terhorst, R. Geha, and F. Alt.